Nov. 7, 2007 -- Women are most attracted to sex with masculine, high-risk
men during ovulation, when they are most likely to get pregnant, a Kinsey
Institute study suggests.

Heather Rupp, PhD, a research fellow at the Kinsey Institute, studied 12
single heterosexual women aged 23 to 28. While hooked up to an fMRI machine
that detects activity in different parts of the brain, the women looked at 256
photos of male faces.

Using a computer morphing program, researchers altered the photos to make
the male faces look more or less masculine. The women were also given sexual
risk information on the men that included their number of sexual partners and
their typical condom-use patterns.

After viewing the faces and the information, the women were asked to rate
how likely they were to have sex with the man in each photo.

But in this study, Rupp and colleagues weren't as much interested in who the
women said they'd have sex with as in what happened inside their heads.

Around the time of ovulation, when the women were most likely to conceive
after unprotected sex, the women's brains showed more activity in areas linked
to reward and risk taking. Stimuli that arouse this area of the brain include
drugs, alcohol, and gambling.

During ovulation, the women also had weaker brain responses in brain areas
linked to inhibition and risk evaluation. And while women showed more activity
in brain areas linked to decision-making and reward when looking at photos of
high-risk men than when looking at photos of low-risk men, this activity was
weaker during ovulation than it was later in the menstrual cycle.

At this week's annual meeting of the Society for Neuroscience, Rupp
suggested that during ovulation, women may be more likely to engage in risky
sex and be more vulnerable to drug and alcohol abuse than at other
times.

"At ovulation, when is likely, women may
prioritize fertilization and find masculine men more rewarding and less
risky," Rupp suggested in her meeting presentation. "Towards the end of
the menstrual cycle, when hormones are preparing for potential pregnancy, the priority may shift
from mating to finding a low-risk, stable partner who can provide more parental
investment and resources."